Bill Freeman wrote:
I'd like a bit of info from some of the RV fliers out there. I'm a bit
spoiled since I fly the Long EZ which can't stall and the C182 which
damn near can't stall (an exaggeration, and I AM careful with it, but
they are very stall resistant), so am a bit of out of touch with the
more
conventional high performance homebuilt state of the art when it comes
to stall behavior. What is the behavior of the RV at a 1G stall and
how different is the accelerated stall? How critical is a centered ball
to the respose at stall? How much does builder variation seem to
affect the stall speed and response?
Does the RV series us any triangular leading edge "stall strips" to
cause
an aero buffet stall warning? Are there any of the new "hi tech" stall
protections (cuffs, vortex generators, slots, etc) recommended, used
or even tested? Was the accident aircraft stock or modified in any
way that might have affected the aerodynamics, esp at high alpha? How
was the accident aircraft set up for CG? Any chance that the CG was
aft? An aft CG generally causes lighter elevator forces, making it
much
easier to pull a bit too hard and cause an accelerated stall. Aft CG
also
causes lower natural pitch stability and a more difficult recovery from
a stall.
It is really a shame to lose friends to an aviation accident - I've been
there,
worked on the crash investigation at the scene, and didn't like it.
Would
rather it never happened again. It seems more frustrating that this is
a very
old accident type, we should all have airplanes that protect us from
this std
accident. This was part of the reason I chose the LE, but please don't
take
this as a slam at the RVs. Just trying to understand the state of the
art for
RVs and stall protection and warning. Seems like the RVs are a nice
airplane with a lot of good performance. I sure hate to seen ANY
aircraft
accidents that might have been avoidable.
We need to learn from this loss of life, maybe somebody will do
SOMETHING
differently and will avoid this same problem.
Bill Freeman
Here are my observations on RV stall characteristics. Your milage may vary
but since we have a lot of future RV drivers here it's worth discussing.
The RV series (except -9) uses the 23012 airfoil which has only a very
subtle buffet just before stall. If you wait to feel strong buffet you will
be on the ground. OTOH, stall recovery is virtually instant and requires
only release of back pressure to recover. From 1 G entry, altitude loss is
minimal (almost 0 ) if release of back pressure is prompt. Even though
there is no washout in the wing I have never noticed any tendency toward
wing drop. Spin entry requires a lot of intentional rudder to induce. My
first accelerated stall was while inverted during a botched loop. Even then
it didn't spin. The C 150 has more stall buffet cue but recovery is
terrifying compared to an RV.
Paul's discussion of increase in drag at 4 G sounds correct but it should be
noted that it only requires 3 - 3.5 G to do a loop in an RV. Hard to
imagine pulling that hard in a pattern situation. These things are very
hard to second guess though. I'm just sorry for the loss of a fellow flyer.
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
I picked 4G because it made the calc's easier :-)
When I get back from Arlington and OSH I might write a program
on it. I am kind of interested. I will also put in the effects
of a little climb on how long it takes to bleed off speed.
I am inclined however to believe the wake vortex theory.
I don't know about an RV but if you initiate a roll in to a tight turn
in a 182 you better pay attention to a bit of rudder and elevator
right now or you will lose altitude fast. Lore has it that during
WW II fighter jocks got naive enemies off heir tail by suddenly pulling a
real tight turn at tree top height. The follower would then
cartwheel in trying to do the same.
Paul Lamar
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